The invention relates to a method for constructing a layer structure on an especially fragile flat substrate. Furthermore, the invention relates to a solar cell as well as to the use of an inorganic ceramic material.
The construction of layer structures in macroscopic as well as in microscopic bodies is sufficiently known. Laminates in the furniture and construction material industry or corrosion-resistant coatings of metals can be mentioned as examples.
Constructing coatings to increase surface hardness to diminish the wear and tear of components in machines is also known.
Coatings are applied and burned in for configuring the surface of tiles in the ceramics industry.
Sheet steel can be enameled in order to make it resistant toward chemical influences and mechanical attacks. At the same time, there results a correspondingly configured surface.
Layer constructions are known from microelectronics in which the individual layers are structured photolithographically and epitaxially generated through gas phases. Functional components are generated as a rule through typical epitaxy layers. Here as a rule polished semiconductor disks serve as substrates which are built up layer by layer.
Applying electrically active layers on the basis of silicon or comparable semiconductors to ceramic substrates is known in the area of solar cell production. With the method particularly coming into use it is a matter of gas phase epitaxy or liquid phase epitaxy in which, for example, molten silicon is applied to ceramic substrates.
According to another method, layers applied to ceramic substrates are subsequently crystallized in order to improve the electrical properties. In the area of photovoltaics these processes serve to spare expensive semiconductor materials or replacing them through more costly ceramics.
The previously known approaches to reducing the thickness of photoelectric layers proceed from a supporting substrate on which the semi-conducting material is built up in the form of one or more layers to form the solar cell though various methods.
Reducing manufacturing costs is of extraordinary significance in order for the photovoltaics to succeed economically. In comparison with electrical energy generated with conventional means, energy obtained from sunlight through solar cells is still too expensive. Material costs contribute a basic amount to this.
Photovoltaics on the basis of monocyrstalline or multicrystalline silicon delivers very good energy transformation effectiveness from sunlight into electrical current in comparison with solar cells from thin photoactive layers which are built up on substrates. The material cost component is moreover primarily determined by the price of monocrystalline or multicrystalline silicon disks. Therefore obtaining disk thicknesses as thin as possible is sought in order to reduce costs. But increasing breakage rates during processing into a solar cell and subsequently to a module goes along with reducing layer thicknesses. The later a disk breaks in a production sequence, the greater the lost added value.
With multicrystalline silicon disks, those obtained from casting a block and subsequent sawing are differentiated from those which are directly crystallized on the basis of the melts as bands or in the form of tubes, for example according to the EFG method (edge-defined film-fed growth). The behavior of these materials is nonetheless different under mechanical loads. As stable a handling as possible with usual methods is necessary for further processing in order to attain a high added value by reducing breakdowns. This in particular applies for thin silicon disks. This is also significant if materials of different manufacture are to be processed with one and the same production line.